Why do motorcycles have to adjust their valves after the running-in period? How to adjust it? How to adjust

All parts of the new car are made of pig iron, and some parts will become loose after burning, cooling and friction. This is what needs to be adjusted, such as chains and valves. Adjusting the valve clearance requires considerable technology, for example, the engine will be unable or unable to start because of disorderly adjustment. I have a set of techniques here. If you are not afraid to fix it, I can teach you. I said I was afraid of being damaged because I was afraid you didn't understand. )